Electrical submersible pumps (ESP) are widely used to pump oil production wells. A typical ESP has a rotary pump driven by an electrical motor. A seal section is located between the pump and the motor to seal dielectric motor lubricant from the well fluid. The seal section may have components to reduce the differential between the well fluid pressure on the exterior of the motor and the lubricant pressure within the motor. A drive shaft, normally in several sections, extends from the motor through the seal section and into the pump for rotating the pump. The pump may be a centrifugal pump having a large number of stages, each stage having an impeller and diffuser.
During operation, the impellers create thrust, which can be both in downward and upward directions. The impellers transmit the thrust in various manners to the diffusers. Some pumps are particularly used in abrasive fluid environments. In those pumps, a thrust runner sleeve is coupled to the shaft to receive down thrust from one or more impellers. A key fits within an axially extending groove in the inner diameter of the thrust runner sleeve and an axially extending groove on the outer diameter of the drive shaft. A bushing secured into a receptacle in the diffuser receives the down thrust and transfers the down thrust to the diffuser. The thrust runner sleeve and the bushing may be formed of an abrasion resistant material, such as tungsten carbide, that is harder than the material of the shaft and the diffuser. The bushing is commonly installed in the receptacle with a press fit.
In wells with extensive sand or well fluid particulate production, wear of the key and shaft wear is a common problem. The sand particles and other abrasives may be smaller than the clearances between the key and the axially extending mating grooves. These particulates can be trapped and cause fretting wear due to torsional vibration. The drive shaft and key are generally of softer material then the material of the sleeve, causing the fretting wear to be more severe in the key and the drive shaft. When the key cannot continue to hold the torque between the drive shaft and the sleeve, it may shear off. The wear then translates from fretting into abrasion between the drive shaft and the sleeve, which accelerates the material removal from the drive shaft. Finally, mechanical shock may break the sleeve or the reduced shaft diameter may no longer be able to deliver the torque required.